Use of fertilizer is essential in supporting the growth of high yield crops. Of the basic nutrients that plants need for healthy growth, large amounts of nitrogen (taken up as NO3− or NH4+), phosphorus (taken up as H2PO4−), and potassium (taken up as K+) nutrients are required by most crops on most soils (Wichmann, W., et al., IFA World Fertilizer Use Manual). Such large amounts of nitrogen, phosphorus, and potassium nutrients are supplied mainly in the form of mineral fertilizers, either processed natural minerals or manufactured chemicals (K. F. Isherwood, 1998, Mineral Fertilizer Use and the Environment, United Nations Environmental Programme Technical Report No. 26).
Despite the importance of mineral fertilizers in providing mankind with abundant agricultural products, the harm done to the environment has been recognized in recent years. Mineral fertilizers may incurred damages to soils. For example, most nitrogen fertilizers may acidify soils, thereby adversely affecting the growth of plants and other soil organisms. Extensive use of chemical nitrogen fertilizers may also inhibit the activity of natural nitrogen fixing microorganisms, thereby decreasing the natural fertility of soils. The long term use of mineral fertilizers may also cause severe environmental pollution. For example, the loss of nitrogen and phosphate fertilizers due to leaching and soil erosion has led to contamination of soil and ground water, and eutrophication of surface water. Cleaning up polluted soil and water has been a complicated and difficult task. The cost for such a task is also astronomical.
In search for a solution to the problem, some are going back to organic fertilizers, such as manure (Wichmann, W., et al., IFA World Fertilizer Use Manual). The use of manure as fertilizer dates to the beginnings of agriculture. Large amounts of manure are produced by livestock. For example, in the United States, farms (including confined animal feeding operations) generate more than 136 million metric tons (dry weight basis) of waste products annually. Manure has value in maintaining and improving soil because of the plant nutrients, humus, and organic substances contained in it. Studies have shown that a high percentage of the nitrogen, phosphorus, and potassium fed to dairy cattle are excreted in manure.
As manure must be managed carefully in order to derive the most benefit from it, some farmers may be unwilling to expend the necessary time and effort. Manure must be carefully stored to minimize loss of nutrients. It must be applied to the right kind of crop at the proper time. In general, manure does not provide all the plant nutrients needed and very large amount of organic fertilizers have to be applied to soil. Thus, there is a tendency to discount the value of manure as fertilizer. Manure may also contain undesirable chemicals, such as antibiotics and hormones. Only in underdeveloped countries, where artificial fertilizer may be costly or unavailable and where labor is relatively cheap, manure is attractive as a fertilizer.
Furthermore, manure may contain significant levels of nitrogen and phosphorous which threaten water resources if not managed correctly. If not stored or disposed of properly, it can pose health and environmental threats. For example, it can cause air pollution, i.e., odor and dust; and contamination of surface and ground water with excess nutrients, organic matter, salts, and pathogens. For example, manure contains pathogenic microorganisms, such as Escherichia coli, Salmonella spp., Shigella spp., and Campylobacter jejuni. 
Biological fertilizers utilizing microorganisms have been proposed as alternatives to mineral fertilizers. Naturally occurring nitrogen fixing microorganisms including bacteria, such as Rhizobium, Azotobacter, and Azospirillum, (See for example, U.S. Pat. No. 5,071,462) and fungi, such as Aspergillus flavus-oryzae, (See, for example, U.S. Pat. No. 4,670,037) have been utilized in biological fertilizers. Naturally occurring microorganisms capable of solubilizing phosphate rock ore or other insoluble phosphates into soluble phosphates have also been utilized in biological fertilizers either separately (e.g., U.S. Pat. No. 5,912,398) or in combination with nitrogen fixing microorganisms (e.g., U.S. Pat. No. 5,484,464). Genetically modified bacterial strains have also been developed and utilized in biological fertilizers. An approach based on recombinant DNA techniques has been developed to create more effective nitrogen fixing, phosphorus decomposing, and potassium decomposing bacterial strains for use in a biological fertilizer, see, for example, U.S. Pat. No. 5,578,486; PCT publication WO 95/09814; Chinese patent publication: CN 1081662A; CN 1082016A; CN 1082017A; CN 1103060A; and CN 1109595A.
However, the biological fertilizers that are based on naturally occurring microorganisms are generally not efficient enough to effectively replace mineral fertilizers. It is therefore important to develop more advanced biological fertilizers that can replace mineral fertilizers in supplying nitrogen, phosphorus, and potassium to crops for producing high quality agricultural products while avoiding the problems associated with mineral fertilizers.
The present invention provides a biological fertilizer based on non-recombinant yeasts, which can replace mineral fertilizers and provide an effective and environmentally-friendly method of using certain organic materials.
Citation of documents herein is not intended as an admission that any of the documents cited herein is pertinent prior art, or an admission that the cited documents are considered material to the patentability of the claims of the present application. All statements as to the date or representations as to the contents of these documents are based on the information available to the applicant and does not constitute any admission as to the correctness of the dates or contents of these documents.